System for testing propellers



A.F.ZAHM. SYSTEM FOR TESTING PROPELLERS.

APPLICATION FILED JULY 6, I918.

1,405,177, Patented Jan. 31, 192 2,

2 SHEETS-SHEET I.

I gmwmtoz ALBEETEZAHM- $511 I alto mm A. F. ZAHM.

SYSTEM FORTESUNG PROPELLERS.

APPLICATION FlLED JULY 6,1918.

Patented Jan. 31, 1922.

2 SHEETS-SHEET 2- ALBERT F. ZAHM.

$5 arrow, 45 W w re stares NT-mm.

ALBERT F. ZAHM, OF VJASI-IIIN'GTON, DISTRICT OF COIIIl'IIIIBIA'.

SYSTEM non {TESTING 'raornninns.

To all whom it may concern."

'Be it known that I, ALBERT F. ZAHM, a citizen of. the United States, residing at ll ashington, D. 0., have invented certaln new and useful Improvements in Systems for Testing Propellers, of which the iollov ingis a specification.

My invention relates particularly to the art of designing and testingfaeronautical propellers; although certain features thereof are equally, applicable to the design of propellers intended for other and various uses.

It has'heretofore been impossible to determine with the required or desired accuracy the actual operating characteristics of the different elements of a propeller blade and accordingly designers have been unable to check or compare the theoretical and'calculated results with the actual results ob tained' in practise. This has resulted in uncertainties and inaccuracies in the design of propellers and the object of my invention is to'remo've this 'diliiculty and avoid to a great extent these uncertainties and inaccuracies of prior designs." In accordance withmy invention, I have devised a system or apparatus whereby the pressure distribution throughout the propeller blade or'blades may be accurately determined and recorded, thereby enablingthe'designer to check up the calculated results and revise his theoretical designs accordingly, if found necessary after comparison with the actual results obtained experimentally;

To this end I embed in the propeller blade one or more ducts whichlead respectively to the one or more points or elements on the surface of a propeller blade where the-tests are to be made, and Iconnect these ducts with a pressure responsive, recording or in (heating apparatus for-experimentally determining the actual wind pressures at the various points selected on' the'face or back of the blade. 7 These ducts may be connected directly withthe pressure measuring apparatus and the pressuresdetermined during the operation of the propeller, as bythe provision of a manometer or other pressure device on' the aircraft and suitable communieating connections between the manometer and the rotating embeddedducts. The con-I nection' with the rotating ducts may take Specification oi Letters Patent. Patented J an, 31, 1922, Application filed July 6, 1918'. SerialNo. 243,659. 7

diate measuring mechanism which may con-.

sist of air pressure containers for? accumulating air from the various testing, points of the propeller blade, the contents of which may be measured to determine the pressure thereof subsequent-to the operation .of the propeller. The duct openings which'ten minateon the surface of the propeller blade preferably lead outwardly at substantially right angles to the blade face or back while The manometer connections, lead the ducts terminate at their other ends in the pressure receivingand measuring devices. Specifically,.these receiving and measuring devices may consist or metallic airtight containers whose communication withthe ducts may be establishedor interrupted by-some such means as shut-ofi'cocks at the will of the operator or the pilot. Thus-the propeller may be operated' at any desired speed while the aeroplane is in flight and'with thereservoirs or receivers openjto the ducts, and

whilethe'motor continues operatingat that speed the containers orreservoi-rs may be shut oif by the pilot, thereby confiningthere Wltlllll air at the pressures of the respective point's'or elements on the blade face connected'with the ducts. The reservoirs may then be, dismounted from the propeller hub or may be dismounted from thepropelle r shaft with the propeller and the hub, and each reservoir may individuallybe connected with manometer tubes "for the measurement of: the pressure of the "confined and entrappedair. In the specific embodiments illustrating the indirect method of attachment'tothe manometer, l have shown the containersas carriedby the propeller'hub and as having petcoclgs to which the manometer tubes may beconnectedQand I haveillustrated a common means, for simultaneously opening and closing the shut-off cocks of all containers,

as is well understood in thisart.

this control means being under the control of the pilot or other operator, but 1t is understood that the invention may be practiced and embodied in apparatus other than the specific devices hereinafter set forth.

For a better understanding of my invention, reference may be had to the accompanying drawings, which illustrate certain embodiments of the many forms my invention is capable of assuming, wherein- Fig. 1 is aside elevation illustrating one embodiment of the propeller shaft, propeller and the pressure testing apparatus, certain parts being illustrated in section,

Fig. 2 is an end view thereof,

Fig. 3 is a side view of one of the propeller blades, V

Fig. 1 is a section on the line 44 of Fig. 3, i

Fig. 5 is a sectional view of a part of the operating mechanism, I

Fig. 6 is an elevation illustrating a second modification of my invention, also partly in. section, I

F ig. 7 is a detail thereof,

Fig. 8 is an elevational view, partly in section, of a'third modification, and

Fig. 9 is a detail thereof.

And Figure 10 is a detailed View of an element of the operating mechanism.

Referring to the drawings where like numerals refer to like parts throughout, 1 indicates the end of a fuselage of an aeroplane which. carries the usual and ordinary bearing housing 2 for the propeller shaft 3. V The propeller 4L illustrated is of the two blade type, and is fixed to the propeller hub-as usual by the transverse bolts 5 which pass through theblades and engage flanges 6 on the opposite sides thereof. The propeller as a whole including the hub, is fixedly mounted on the reduced end of the shaft 3 Each propeller blade has embedded therein a plurality of ducts 7, and in the specific instance illustrated, there are four of such duct-s in' each blade,the ducts in one blade only being shown, since the ducts are duplicated. in the two blades. These ducts 7 .lead to the different points or elements of the blade face that are to be tested out,and it is understood that these points or elements may be located at various positions selected over the entire face of the blade. .In the embodiment here shown (see Fig. 3) the four points for the respective ducts 7 are positioned substantially in the center line of the propeller blade and are denominated 8, 9, 10and 11, respectively. The ducts at these points open out; through the face of the propeller and preferably lead outwardly at right angles to the face." These ducts 7 may be in the form of light copper or. steel tubes of very small diameter, and maybe conveniently embedded in the propeller blade by first forming a small shallow groove or trench 12 longitudinally of the face of the blade which is illustrated in the drawings as flared out at the bottom of the blade to permit the spreading of the ends of the tubes. The tubes or duct-s 7 are disposed within the groove, and the groove is then covered or bridged by a thin strip of suitable material as veneering 13. This strip 13 rests upon a shoulder 12 surrounding this groove and is fixed to it in any convenient manner as by gluing. The strip 18 forms a surface continuous with the face of the blade, so that there are no interruptions or irregular surfaces to interfere with the proper or normal operation of the blade. It is understood that this strip 13 is provided with openings at 8, 9,10 and 11 substantially of the diameter of the ducts 7, which openings register with the collecting ends there of. The ducts 7 at the bottom of the blade lead outwardly from and transversely of the blade face and extend horizontally L to the rearward ends of cylindrical containers '14,

15, 16 and 17 respectively, these containers or pressure receiving reservoirsbeing of light metal and being: provided with individual shut-off cocks 14, 15, 16" and 17. respectively. The ducts 7 after emerging from the propellerblade communicate with the containers through these shut-off cocks, whereby communication may be established or interrupted betweenthe ducts and the containers at the will of the operator or pilot. The containers are also\ provided with. means for connection with pressure responsive apparatus, as for instance a manometer tube, and, as shown, this means of attachment comprises petcocks and 1107.:

zles 18 leading outwardly through the ends of the containers. The containers are conveniently carried by the propeller hub. and

for this purpose the hub on its rear end is provided with a plate or carrier 19, which encircles the shaft 3 and is clamped to the hub by means of the bolts 5 as illustrated in Fig. l. This plate19 carries on its periphcry a receptacle or other supporting member 20 for each of the containers or reservoirs, and these supporting members 20 preferably correspond in shape'to the exterior of 'the containers and are also preferably formed integral wit-h the plate 19.;For actuating the shutoff cocks there is provided an operating mechanism which comprises a ring 21 surrounding the bearing housing 2 and can ried'by the;- plate or carrier 19. For this purpose the ring 21 has formed on the opposite ends of the diameter a pair of'barrels or cylindrical members 21', these members extending parallel to the shaft 3 and receiving plungers 27 carried by arms 28 which extend outwardly from the plate 19. The ring may thereby receive axial movement'for engaging andactuating the spring pressed valve stems 22, each member 21 being provided barrel 21/. also has afcompression spring'3O disposed behind theplunger 27 for normally maintaining the ring 21 out of engaging relation with the valve stems. These valve stems 22 are provided with compression springs 22 for the purpose of normally maintaining the shut-off cocks in a closed position, that is the'cocks aremaintained closed except-when engaged and actuated by the ring 21. Disposed-on some convenient part of the fuselage is'loca-ted a rock-shaft 23 which extends transversely of the bearing 2 and slightly therebelow. On each'side of theibearing the rock-shaft'23 is provided with an upwardly extending arm 24: (preferably integrally formedthereon) and these arms carry actuating rollers 25 for engage-- ment with the ring 21 as illustrated in Figs: 1 and 2. The shaft'23 also carries a crank arm 2Q which may be connected with the operators control lever by means of con necting links, these connecting devices not being shown in the drawings for convenience in illustration. .It is understood, how-' ever, that the operator or pilot-at any time during the flight may actuate the shut-off cocks through the medium: of therock-shaft 23 and actuating rollers 25, the. shut-off cocks 14!, 15 16 and 17 thereby being operated simultaneously. vz

When it is desired to determineIt-he air pressure on the propeller blade at the various points selected andindicated, the pilot, through the medium of the; rock-shaft 23 and 7 other actuating devices illustrated, forces the ring 21 as a unit toward the propeller and thereby operates the various cocks 14k, 15, 16' and 17'" against the tension of the closing springs 22' which surround the valve stems. When these shut-01f cocks are opened, the containers-receive and accumulate air from the mouths ofvtheir-respective ducts 7 this accumulated air being at the pressure corresponding to the various points or elements 8, 9,10 and 111011 the propeller blade, and after they. are permited 1 to collect air' for a sufiicient' length of time to become filled with air at the pressures corresponding to the various points, the operator then withdraws the camrollers from engagement with the ,ring. 21', thereby permitting the shut-off cocksto be closed by'their' corresponding springs 22'. The flight is then discontinued and the air containersare connected up with a suitable pressure responsive and in dicating apparatus, as by means of manometer tubes attached tothe petcocks '18, whereby the pressure of the air entrapped in each cylindrical container may be indi vidually measured and; determined. The containers may be removed from the fuse lag-e of the'machinewith the propeller as aunit, or if desired, detachable connections 31 might be provided in the horizontal portions of the tubes between the containers or shut- 0a cocks and the ducts 7 whereby the containers individually maybe removed from the mounting and the air pressures therein determined. It is understood that the clearance' between the stems-22 andring {21 in its retracted position is sufficient 'to permit the removal of the'detachable connections 31 without opening 'the' cocks.- 5 After removal of these connections thecontainers may be rotated in their receptacles so as to bring the valve stems 22 out of the'pa-th of'the' ring 21 (starting at either end) and the containers may then be removed a rially'from' their receptacles or holders.

. y' pp s for exploring the surface --of' a propeller blade is illustrated in Fig 6, whereinis shown a housing 33 for'the bearing of the propeller shaft 34, the' pro'peller 35 being ipdica'ted as securely anohoredand fixedto tie bolts 37 are illustrated for securely clamping the propeller-35 between"o pposed plates '38 e and tea flange 39 formed integrally-"on the propeller shaft 3.4; It is understood, how: ever, that the particular propeller mounting forms i no part of the invention claimed in the' present application. The ductsf em- A second modification of propeller hub sleeve 36.; A number of 7 bedded in the propeller blade'areindicated at 40 and at theirinner ends terminate in the right angle POltiQIlSlQ. For supporting and carrying the demoun'table pressure being extended beyond theopposite side of the propeller 35 to form an GXtGIlSlOIIBi" which carries the containers 43 and the actu -j wise suitably assembled in-fiXed position.

The containers 43 on their inner en'ds are provided with connections 46 which are adapted "to c'omrnunicatingly register with:

the right angleportions '42 of the-embedded V ducts 40-when the unit is' assembledonthe extension "34'." An 'annulan'member' 47 (preferably of Wood) is fiXed-ftothe outer side o-f'the propeller" around the shafteX- tension 34, the portion thereofnear the periphery being provided with transverse openings for the reception of the right angle" portions 42 of the ducts, these ducts extending therethrough and slightly beyond in dicatedin'fthe drawings. One side of-this member 4E7 is provided with transverse openings for the reception of the heads of the I00 containers 43 the shaft -3 lis illustrated as bolts 37 whereby. the member 47 may'be brought secu'rely into engagement with the outer clamping flange '38 and a driving connection therebetween may be formed. ,A container unit is brought into operative position by inserting the sleeve144 over the extension 34, bringing the containers 43 with their. connections 46 in alignment and registering With the ducts 42. For establishing an air-tight connection between-the. containers 43 and the ducts 42 there is provided a rubber plug48 which has an openingpassing therethrough for the reception of the. connections 46;and the ducts 42 and isadapted to be wedged tightly between the connections 46 and the member 37 as indi- ';cated in Figs. 6 and 7, the extension 34 being-provided with a clamping nut 49 for drawing these parts together in a'manner to secure. an alr-tight fitting. E or providing-a 7 positive driving connection between thecontamer unit-and the member 47 there are pro-.

vided a plurality of driving'members or rods 50 which pass transversely through the member 47 and the inner plate 45,- 'as indicated. The connections 46 are provided 'wi'th shut-off cocks 51 which maybe opened or closed to establish or interrupt communication between the containers 43 and the ducts 40. .In a manner similar to the :arrangement of Fig. .1, operatingdevices are provided whereby these shut-off cocks may be controlled from the operators seat on the aircraft. For this purpose the shut-off cocks 51 are provided with operating links 52 avhich are ,in turn connected to eyes formed in the transverse flange on a sleeve 53,,- the I latter being slidable back and I forth on the sleeve 44 foropening-and closing the valves. A stop 54 is provided for limiting the outward movement of this actuating sleeve- 53, .a spring 54 being provided around the sleeve 44 and being disposed between the inner circular plate 45andthe sleeve53for constantly urging. the sleeve 53 inan outward direction to close the shut-off cocks 5l.- The cocks 51 may be simultaneously opened'and latched in the open position by means of a latch member comprising a standard 55wcarried' by an integral spring arm or latch 57 attached, as at 56 to the inner side of the plate 45,:illustrated in Fig. 6.

.Thislatch maybe sprung into engagement the hub; flangewith its outer end in engagement withan abutment or ear. formed on the leads to actuating spring 54 until thespring1trigger157snaps,

over the flange'on'the end of this sleeve.

This is done, 'of course, before the motor and propeller are started. Afterihe ma chine; has been started and the propeller is operating atrthe required Stestspeed, the operator or pilot pushes outwardly on the connecting link 60} thereby causing the tri-p lever 59 to take apositioninthe path of the end of the'push rod 58 and this, push rod in turntrips the latch 57 through the a medium of the standard '55:;which-is formed a part thereof. Upon" the release of the sleeve 53the spring 54 causes an automatic closure of all-the shut offcocks thereby enclosing or trapping air in the containers 43 at the pressures corresponding to the various points on the surface of the propeller being'explore'd. The machine thereupon is brought to rest and'the containing unitremovedfrom theshaftextension 34 by removal of the nut 49 whereupon the pres sures of the various containers may be measured and determined by connecting the manometer or other pressure'responsive orindicating devices with the=nipp'lesson the 7 end of the connections 46, the:measuring of "the pressure in these containers being ac comphshed 1n amanner'similar to thatof the modificatlon illustrated in Figs. 1 *to5.

In Figs. 8 and.9I have illustrated another modification of my invention, this modification being particularly distinguished from the above described"modificationby the provision of means-for measuring thepressures on the surface of a propeller-blade during. the operation thereof instead of trapping the air in ressure 'zconta-iners and subsequently measuring the pressure of .the entra'ppedair i as setforthcabove. In accordance-with this modification the measuring apparatus has a manometer connected directly with exploring ducts onthe surface of the propeller blade while the propeller is operated, where by'at any time-while;the-propeller is being operated and at anyspeedthe windpressures thereon may be determined by a simultaneous inspection of theymeasuring apparatus or by other appropriate means. For accomplishing this purpose I d-ispose'on the propeller shaft a stationary sleeve 61,-this' sleeve being of a 'cylindricalexterior form and having and flanges 62 formed integrally therewith and serving as bearing members against the shaft 63. The interior'of this cylindrical sleeve-61 is provided with a plurality of radial circular flanges 64 and alternating with these flanges or rings 64 are a plurality of sealing flanges 65in'dicated in the present instance as formed integrally I on the shaft 63. These sealing flanges 65 are of a circular form and project into proximit to the periphery of the sleeve 61 there by ferming a multiplicityof chambers 66 around the shaft 63, disposed between these sealing. flanges. For insuring an airtight seal between these'various chambers 66, .a sealing liquid 67 is contained in the chamhers enclosed-by the sleeve 61 which upon rotation of the shaft 63 at the operating speeds of the propeller is thrown out by centrifugal force against the interior of the periphery of the sleeve61 in the manner indicatedtoefi'ect a perfect seal between the flanges 65 and the sleeve. The annular chambers 66 are thereby providedaround the shaft 63, each of them being effectively sealed against the outside atmosphere of the other chambers. The exploring ducts, which it is understood are embedded in the propeller blade in a manner similar to that indicated in the above described modifications are indicated at 68, these ducts passing radially down the propeller blades to the end of the shaft and thence inwardly and longitudinally through the interior thereof, the shaft beinglmade hollow for this purpose.

The inner ends'69 of these ducts are bent at right angles tothe shaft 63 and are sealed in transverseopenings-therein leadingto the v annular chambers 66I'iOne of the measur- 40 111g7 devices is :.illustrated diagrammatically at O and is indicated as having .a connection 71 leading to. the stationary pipe or duct connection 721v Thesestationary ducts 72 pass transversely through'the sleevehousing indicated diagrammaticallyat 7 3, transversely through the sleeves 61 and through the rings 64:, terminating. in the annular chambers 66: In accordance with this modification the ducts 68 lead the wind pressures collected at the various exploration pointspn the propeller surface to the accumulating chambers 66, and accordingly these chambers ac-l cumulate-air at pressures corresponding' to the pressures on the elements of the propeller blade. The manometer 70, or other pressure responsive devices, is used to indicate the pressure of'the accumulated airin these annular chambers 66 and accordingly the wind pressures on the various points selected on the propeller bladesmay be. de-, terminedand recorded duringand while the propeller is running-at anyparticular speed and-load desired for the tests, it being understoodthat the devices are more or less diagrammatically illustrated and. that the sponsive device.

designs and proportions and location th rer of may be variously modified to suit the different requirements met with inpracticeh Th'e pressures at the various points selected having been experimentally determined,

the theoretically calculated or expected values, and if the theoretical and the experimentally determined results are widely at variance, the designer is in a position to make the necessary changes in and revisionof his designs. A propeller may thus be ob.-- tained whose efficiency and operating'characteristics are in accordance withthe ex Pected values. a p 1 I I have thus set forth one complete embodiment of my invention inthe specific manner required-by the patent statute's, but: it is un derstood that the claims annexed hereto are not to be'limited to the specific devices illustrated inthe drawings except as is specifically recited thereon, but are to be given a scope commensurate with the spirit-of the invensure-distribution on'the surfaceofa propeller blade, the combination of aduct embedded in the'propeller' blade and terminating at one end at a point on the surface of'the'bladeg-with means at the other: "end of the duct for attachment toa pressure re '2. In a system for determining the' pressure distribution on thesurface of a pro peller blade, :the combination of a duct embedded in'x'the propeller blade,}said duct opening outwardly at one end at 'a-point on the surface of the 'blade,? with means at the other end of the duct' for' attachment to a pressure IGSPOIlSlVQdQVlCfi.

1. In a: system for determining 'the pres- 4 I '3. In asyst'em for determining-the presi sure distribution on the surface of a propeller blade, the combination of a plurality ofducts embedded; in the'propeller blade and terminating at one; end at different points on the surfaceoffthe blade-, wi'th points on the surface of the blade,said ducts opening outwar'dlyat right angles to'fthe 7 surface face, with means at the other'ends of the ducts forattachment to a pressure responsive device.

5. In a system for deterinining-the pressure distribution on the surfaceof afpropeller blade, the combination of 'a plurality of ducts embedded beneath the surface of the propeller blade and terminating at one end at different points on the. surface of 70 the results obtained may be compared with r the blade, with means'at the other endof the ducts for attachment to apressure responsiverdevice. V

6. A system for determining the pressure 6 distribution on the surface of a propeller blade, the combination, of a plurality of;

ducts embedded, beneath the surface of the propeller blade and terminating at one end and opening outwardly at different points on the'surface of the blade, with means at the other end of the ducts for. attachment to a pressure responsive device. l v v 7. In asystem for determining the pressure distribution on a face of a propeller blade, the combination of a plurality of ducts embedded in the propeller; blade and terminatingat one end in mouths opening outwardly substantially at right angles to the face of the blade at, different: points thereon, with means at the other end of the ducts for attachment to a pressure responsive device. 1

' t 8. In a system-for determining thepressure distribution on the face of a propeller blade, the combination of a duct embedded in the propeller blade and terminating at one end, at a. point on the face of the blade, with means at the other end, of the duct for attachment to a pressure registering means.

80 1 9. In a system for determining the pressure distribution on the surface of'a propellerblade, the'combination ofa duct embedded in the propeller blade and terminating at one endiat a point on the surface of the blade, with means at theother end of the ductfor receiving the air under pressure r taken from the surface of'theblade' while in operation.

a propeller blade having on the: surface thereof an air collecting inlet or mouth and a communicating passage therein leading vice. V a

11. Ina systemfor-determining the pressure distribution on the surface of a propeller blade, the combinations of a plurality of ducts, embedded in the propeller blade and terminating at one end'on the surface of the blade, with means at the other end of the ducts comprising a rotating and a stationary member for attachment to. pressure responsiiitlesdevices during the operation of the. pro

e 7 er. s e p 12.. In a systemifor determining the pressure distribution on the surface of'a pr0- peller blade, the combination of aplurality of ducts embedded in the propellerblade and terminating at one end on different points ofthe surface of the blade with means comprising a plurality of communicating chambers for attachment to a pressure responsive device during the "operation of the propeller, ,7

from said inlet to a pressure responsive de-- '65 '13.,In-a' systemior determining the pres 10.,In an apparatus of the type set forth,

sure distribution on the surface of propeller blades, the combination of a duct embedded in the propeller blade and leading at one end to the point on the propeller surface tobe explored, with means at the other endof said duct for accumulating airpressureduring the operation of the propellerblade, and a pressure responsive and measuring device comprising means for communication with said first mentioned means during the opera ation of the propeller. V 1 14. In a system for determining thepressure distribution on the surface of thexpropeller blade, in combination,v aplurality of ducts embedded in the propeller blade, said ducts terminating at one end on the different points of the blade to be explored and termi nating at the other end in'annular chambers formed between a'plurality ofaxiallyspaced flanges formed on the propeller: shaft, a stationary member surrounding said flanges having a plurality of radially disposed rings, said rings alternating with said flanges and projectingradially inwardly within said annular chambers, means for sealing the said chambers against each other,'and a pres-v sure responsive apparatus having duct connections leading downwardly to'said sealed chambers for. the purpose set forth. 7 15. In a system for determining the pres-l sure distribution on the surface of a pro peller blade, the'combination of a duct em bedded in the propeller blade and terminating at one end on the surface-of the-blade, said duct passing axially of theprop'eller shaft and terminating on the periphery thereof between a pair ofltransverse flanges formed thereon, a'sealing-inember surround ing said shaft and said flanges, said member 7 having three radially disposed ringsxalter- 1 05 natingv withand enclosing said flanges, a sealing. liquid contained within said sealing member and. adapted to seal the annular space-between said vflangesand said sealing member and a pressure responsive device having alduct connection leading through the intermediate one of said rings .torthe an nular chamber formed thereb y'between said flanges and in communication with said exploringduct. I r 16. In a system for determining the pressure distribution onzthe surface of a prof pellerrblade, in combination, a hollow propeller. shaft having aplurality of. axially spaced transverse circular flanges on the exterior thereof, a propeller mounted "onsaid shaft and having embedded thereina plu-; rality of exploring ducts; leading: at one end to different points onxthe surface of'thepropeller and at the othersend to the: annular 125 spaces or. chambers formedon -theiexterior V of said shaft between said transverse flanges, a stationary cylindrical member-xhavl'ng transverse bearingmembers on the end-there: of engaging thesaid shaft and enclosing said 1180 transverse flanges, said member having a vices having connections leading transplurality of sealing rings on the interior versely through said member and through thereof, which alternate with said flanges said sealing rings to said annular chambers 10 and project inwardly therebetween toward in communication with said exploring ducts.

the periphery of said shaft, a sealing liquid In testimony whereof I hereunto aflix my contained within said enclosing member, signature. and a plurality of pressure responsive de- ALBERT F. ZAHM. 

